The Russian parliament finally approved the Start II nuclear arms reduction treaty yesterday, more than seven years after the agreement was signed and four years after it was ratified by the US senate.

Russia's belated ratification should lead to thousands of American and Russian nuclear warheads being scrapped, and clear the way for more radical arms cuts. But whether that will happen remained unclear last night as further discord loomed over the next stage of the disarmament process.

The ratification vote was accompanied by a stern threat by President Vladimir Putin to pull out of arms negotiations altogether if the US proceeds with the planned development of its missile defence system, in contravention of the earlier ABM (anti-ballistic-missile) arms pact.

The former Russian president, Boris Yeltsin, tried for six years to get the Start II treaty endorsed but repeatedly came up against the communist majority in the lower house, the Duma. Yesterday's 288-131 vote was the first demonstration of Mr Putin's power in the new Duma, and gave him a crucial boost on the eve of his debut on the international diplomatic stage.

Making an unexpected visit to the Duma to urge deputies to support ratification, Mr Putin said that Russia could not afford to be dragged into a global arms race. "We had one before, and if we allow it again it will be even worse," he said.

He told them that approving the treaty was the best way of ensuring Russia's security, and reassured deputies that Russia would still have sufficient weapons to destroy any enemy "several times over".

Ratification would let the Russian armed forces concentrate their meagre resources more efficiently, he said.

"It will preserve a powerful nuclear shield, but also allows us to channel funds to the support of conventional forces, allowing us to make our army more combat ready."

Start II is intended to halve the US and Russian nuclear arsenals from 6,000 warheads to between 3,000 and 3,500 each, and to enable both countries to intensify their efforts to work out a new treaty, Start III, requiring further cuts.

The communist factions in parliament voted against ratification yesterday, arguing that it would fatally weaken Russia and give Washington a huge military advantage, but they lost their majority in the assembly in last December's elections. A large group of communist activists protested outside the Duma with banners denouncing Mr Putin and the US.

Gennady Zyuganov, the communist leader, described the vote as not "ratification of a treaty but the decisive disarmament of the country". Russia was destroying rockets which could have protected its security for another 15 years, he said.

Mr Putin had made approval of Start II a priority, and its ratification will ease his meeting with Tony Blair in Britain on Monday, and the foreign minister, Igor Ivanov's negotia tions in Washington later this month.

Nevertheless, Washington's wish to amend the 1972 ABM treaty, which it argues is essential if the US is to shield itself from rogue states such as North Korea, Iran and Iraq, is likely to lead to further conflict.

Moscow has refused to contemplate amending the treaty, on the grounds that an enhanced missile defence system in the US would weaken Russia's ability to ensure the "guaranteed destruction" of the US in the event of nuclear war: the factor which theoretically prevented the two countries attacking each other throughout the cold war.

Should the US try to alter the ABM treaty, Mr Putin warned, Russia would "withdraw not only from the Start II treaty but from the whole system of treaties on limitation and control of strategic weapons".

The Duma approved a non-binding resolution stipulating that Russia will have the right to revoke Start II if Washington breaks the ABM treaty. Another non-binding clause gives Russia the option to back out if Nato deploys nuclear weapons in countries that have joined the alliance since 1999: the former Soviet satellites Poland, Hungary and the Czech Republic.

Many Russian missiles are past their service life and will soon have to be scrapped anyway. The government cannot afford further heavy spending in this field, and its defence minister said yesterday that its limited military funds should instead be focused on new modern arms such as the Topol-M land-based missile, a submarine based version, and a new cruise missile for its strategic air force.